Hi, I have a Trane XB80 forced air gas furnace model TUE060A936L1. The furnace runs fine when first coming on but after its warm it cycle on and off. The blower comes on then the gas/flame comes on after a few seconds the flame goes off followed by the blower they remain off for a few more seconds then the cycle starts again. It will cycle many times before finally staying on and running. What could be the cause of this cycling?